1. Field of the Invention
The present invention is directed to a new process for the production of composite structures by the thermoplastic shaping of an assembly based on at least two flat thermoplastically shapable plastic materials arranged in layers one above the other and optionally reinforcing lower, upper and/or intermediate layers, wherein the plastics materials are based at least partly on selected polyisocyanate polyaddition products. The present invention is also directed to the composite structures obtained by this process.
2. Description of the Prior Art
Thermoplastic polyurethane elastomers are known (see e.g. Becker/Braun, Kunststoff-Handbuch, Volume 7, "Polyurethane", publishers Carl Hanser Verlag, Munich/Vienna (1983), pages 406 et seq). Previously known thermoplastically workable polyurethane elastomers are based on diisocyanates, relatively high molecular weight dihydroxyl compounds, in particular relatively high molecular weight polyester diols, and low molecular weight diols as chain lengthening agents. It was previously believed that the polyurethanes should be linear in structure, i.e., they should have no cross-links or branch points in the molecule. It has also previously been recommended that diamines should not be used as chain lengthening agents for the production of thermoplastically shapable polyurethane elastomers (see the reference book mentioned above, page 406, paragraph 8.2.1) because diamine chain lengthening agents incorporate urea groups in the molecule. The urea groups are regarded as hard segments which would prevent thermoplastic shaping of the product.
It has now surprisingly been found that polyisocyanate polyaddition products which have been prepared from branched, relatively high molecular weight starting components containing isocyanate-reactive groups, in particular those in which the number of urea groups exceeds the number of urethane groups, can be thermoplastically processed and, thus, are suitable for the production of composite structures produced by thermoplastic shaping.